The present invention relates to an angular velocity detection device for sensing the angular velocity of a mobile unit such as a vehicle.
The present application claims priority from Japanese Patent Application No. 2003-067324, the disclosure of which is incorporated herein by reference in its entirety.
In recent years, vehicle-mounted navigation systems combine the GPS positioning using the GPS (Global Positioning System) and the autonomous navigation using an angular velocity detection device in the form of hybrid positioning so as to compensate for the drawbacks of the GPS positioning and the autonomous navigation. The navigation system then performs map matching for the resulting position information in map data, thereby determining the current location of the vehicle.
Now referring to FIG. 1, the aforementioned angular velocity detection device is designed such that the angular velocity detection device 1 is incorporated into a vehicle-mounted navigation system to detect an angular velocity ωy of the vehicle in its traveling direction (more specifically, in the direction of yaw). An angular velocity conversion portion 3 multiplies a sensor output ωgyro of an angular velocity sensor 2 (i.e., an angular velocity detected by the angular velocity sensor 2) by a sensitivity coefficient K to find the actual angular velocity ωy of the vehicle. Then, an integrator 4 connected to the angular velocity detection device 1 integrates the angular velocity ωy with respect to time to determine an azimuth Φ of the vehicle.
That is, suppose that the vehicle-mounted navigation system is mounted in the passenger compartment. In this case, assuming that the detection axis of the angular velocity sensor 2 is oriented in the vertical direction P (the direction of gravity) as schematically illustrated in FIG. 2A, the angular velocity sensor 2 is fixed in the vehicle-mounted navigation system.
Accordingly, the vehicle-mounted navigation system mounted in the passenger compartment under this assumption allows the angular velocity sensor 2 to have its detection axis oriented in the vertical direction P (i.e., along the normal to the horizontal plane), thereby making it possible to detect the actual angular velocity ωy of the vehicle with high accuracy. That is, when the aforementioned assumption is satisfied such that the detection axis of the angular velocity sensor 2 is oriented in the vertical direction P, the sensor output ωgyro of the angular velocity sensor 2 shown in FIG. 1 becomes a sensor output ωp shown in FIG. 2A. The angular velocity conversion portion 3 multiplies the sensor output ωgyro (i.e., ωp) by the sensitivity coefficient K, thereby allowing the actual angular velocity ωy of the vehicle to be sensed with high accuracy.
However, vehicle-mounted navigation systems are mounted in the passenger compartment in consideration of the visibility and the operability available to the passenger, the layout of the passenger compartment and the like. Thus, in practice, many of the systems are installed, contrary to the aforementioned assumption, at a pitch angle (hereinafter referred to as the “setting angle”) θset relative to the traveling direction of the vehicle.
In this case, the detection axis of the angular velocity sensor 2 is also oriented in the direction Q tilted by the setting angle θset from the vertical direction P, such that the sensor output ωgyro of the angular velocity sensor 2 shown in FIG. 1 becomes a sensor output ωq shown in FIG. 2A. This causes the aforementioned sensitivity coefficient K to have an error with respect to the sensor output ωgyro, so that the multiplication of the sensor output ωgyro (i.e., ωq) of the angular velocity sensor by the sensitivity coefficient K would not allow the actual angular velocity ωy of the vehicle to be detected with high accuracy.
As shown in FIG. 1, to correct the error in the sensitivity coefficient K resulting from such a setting angle θset, the conventional angular velocity detection device 1 is provided with a relative orientation change calculation portion 6 for calculating a relative change in orientation ΔΦgyro from the sensor output ωgyro of the angular velocity sensor 2, a relative orientation change calculation portion 7 for calculating a relative change in orientation ΔΦgps from the position information Φgps provided by a GPS positioning portion 5, and a learning device 8 for determining the difference (ΔΦgps−ΔΦgyro) between the changes in relative orientation ΔΦgps and ΔΦgyro and learning the sensitivity coefficient K based on the difference (ΔΦgps−ΔΦgyro) to thereby correct the error in the sensitivity coefficient K.
On the other hand, as schematically illustrated in FIG. 2B, suppose that the vehicle travels along an inclined road such as an uphill or downhill. In this case, the angular velocity sensor 2 is also tilted, e.g., at an angle of inclination θinc relative to the horizontal plane, causing the detection axis of the angular velocity sensor 2 to be oriented in the direction R tilted by the angle of inclination θinc relative to the vertical direction P.
Accordingly, a vehicle traveling along an inclined road would cause the sensor output ωgyro of the angular velocity sensor 2 shown in FIG. 1 to become the sensor output ωr shown in FIG. 2B, resulting in the aforementioned learned sensitivity coefficient K having an error with respect to the sensor output ωgyro (i.e., ωr). Thus, the multiplication of the sensor output ωgyro (i.e., ωq) of the angular velocity sensor by the sensitivity coefficient K would not allow the actual angular velocity ωy of the vehicle to be detected with high accuracy.
Suppose also that the vehicle travels along an inclined road having the angle of inclination θinc with the angular velocity sensor 2 remaining tilted at the setting angle θset. In this case, the orientation of the detection axis is tilted at a total angle (θset+θinc) of the setting angle θset and the angle of inclination θinc relative to the vertical direction P. This causes the error in the sensitivity coefficient K relative to the sensor output ωgyro to become more noticeable, so that the multiplication of the sensor output ωgyro of the angular velocity sensor by the sensitivity coefficient K would not allow the actual angular velocity ωy of the vehicle to be detected with high accuracy (See Japanese Patent Application Laid-Open No. Hei 5-187880).
The aforementioned method of compensating the sensitivity coefficient K using the learning device 8 includes an error component in practice. However, while the vehicle is traveling where it can receive GPS signals coming from GPS satellites, an appropriate compensation can be made on the orientation obtained by integrating an angular velocity in accordance with the absolute orientation and positioned location provided by the GPS position information. Accordingly, the method makes it possible to maintain the actual directional accuracy of the vehicle, thereby locating the current position with accuracy.
While the vehicle is traveling where GPS signals cannot be received, it is impossible to make the compensation in accordance with the absolute orientation and the positioned location provided by the GPS position information. In this case, reference is made to a map database for map matching to make an appropriate correction, thereby allowing the accuracy of orientation to be ensured and the current position to be located with accuracy.
However, under the circumstances in which data such as the aforementioned known orientation or positioned location cannot be used, errors in the orientation obtained by integrating angular velocities are accumulated, thus resulting in a lowered degree of orientation accuracy and location accuracy of the current position.
For example, suppose that a vehicle is running in a tunnel, in an underground parking lot, or on a highway ramp, where GPS signals cannot be received. In this case, errors in the actual angular velocity ωy of the vehicle are accumulated, thus resulting in a lowered degree of orientation accuracy and location accuracy of the current position as well.
Furthermore, suppose that a vehicle is running along an inclined road in a tunnel, on a curved highway ramp, or along a curved ascending/descending passageway provided in a spiral fashion in a multi-storied underground parking lot, etc., where GPS signals cannot be received. In this case, when the vehicle makes a turn while running along an inclined road, the error of the actual angular velocity ωy of the vehicle is further increased, thus resulting in a lowered degree of orientation accuracy and location accuracy of the current position as well.
That is, when a vehicle makes a turn while running along an inclined road where GPS signals cannot be received, the angle of inclination θinc being varied every moment and the setting angle θset exert an effect on a sensor output ωgyro, which is delivered from the angular velocity sensor 2, thus causing the sensor output ωgyro and a learned (corrected) sensitivity coefficient K not to be correlated with each other. This makes it difficult to sense the actual angular velocity ωy of the vehicle with high accuracy and causes errors to be accumulated in the orientation obtained by integrating an angular velocity, resulting in a lowered degree of orientation accuracy and location accuracy of the current position.
That is, as described above, a vehicle traveling along an inclined road using the sensitivity coefficient K would cause the angular velocity sensor 2 to deliver a sensor output ωgyro affected by the angle of inclination θinc being varied every moment and the setting angle θset. This causes the sensitivity coefficient K to have an error with respect to the sensor output ωgyro. For this reason, this makes it difficult to sense the actual angular velocity ωy of the vehicle with high accuracy even when the angular velocity conversion portion 3 multiplies the sensor output ωgyro of the angular velocity sensor 2 by the sensitivity coefficient K. This also causes errors to be accumulated in the orientation obtained by integrating an angular velocity, thus resulting in a lowered degree of orientation accuracy and location accuracy of the current position.